The Lymphatic System:
The lymphatic circulatory system is a complex network of thin-walled
vessels responsible for transporting lymphatic fluid collected from the
interstitial tissues of the body back to the heart (Figure 1a) .
Lymphatic fluid is propelled by both the intrinsic contraction and
relaxation of lymphatic vessels and by external compressive forces of
skeletal muscles.[1] Lymphatic fluid is composed of protein, fat,
immune cells (primarily lymphocytes) and excess fluid collected from the
soft tissues. Chyle is the fat and protein rich lymphatic fluid produced
in the small intestines and makes up about 50% of the lymphatic fluid.
Chyle contains high concentrations of long-chain triglycerides,
lymphocytes, electrolytes, immunoglobulins, albumin, fibrinogen, glucose
and fat-soluble vitamins.[2] Intestinal lymph drains to regional
nodes and joins hepatic lymph through the cisterna chyli to feed into
the thoracic duct. The thoracic duct is the end of the central lymphatic
highway that transports lymphatic fluid to the left subclavian vein and
back the blood circulatory system. The thoracic duct originates from the
cisterna chyli around the level of the first and second lumbar
vertebrae, lateral to the aorta (Figure 1a) . Lymph nodes
function to regulate the content of lymph and can activate an immune
response when triggered by a pathogen.